A properly designed radon mitigation system can produce a dramatic and lasting reduction—even when a home begins with a very high radon level.
ATMOS guarantees that the systems we install will reduce the home’s long-term average below 75 Bq/m³. Many homes settle substantially lower, but the final result varies with the foundation, basement finish, accessible sealing, sub-slab material, weather, and other site conditions.
The important point is that high radon is fixable. Active soil depressurization is a proven and predictable method that prevents radon from accumulating inside the home.
Real ATMOS radon mitigation results
The following before-and-after readings are selected examples already shared publicly by ATMOS customers. Names and locations have been omitted for privacy.
These three examples show reductions ranging from 88.5% to 98.6%, with a simple average of 92.4%. They illustrate what can be achieved, but they are not a statistical average of every ATMOS installation and should not be treated as a prediction for a specific home.
How quickly do radon levels fall after installation?
Homeowners with an electronic monitor will often see a substantial change within the first 24 hours after the system is activated. After approximately 48 hours, ATMOS commonly sees the reading fall far below the 75 Bq/m³ guarantee.
Radon changes from hour to hour and day to day. Health Canada recommends beginning the initial post-mitigation short-term test at least 24 hours after the fan is activated, followed by a long-term test to confirm levels through changing conditions.
What post-mitigation level is typical?
ATMOS has seen some homes reach single-digit readings during summer. During winter, many of our completed homes commonly measure in the 20 to 35 Bq/m³ range, although readings can be somewhat higher during periods of very cold weather.
These are common field observations, not guaranteed seasonal targets. Every home responds differently, and temporary changes in weather or pressure can move the reading up or down. The ATMOS performance guarantee is based on keeping the long-term average below 75 Bq/m³ while allowing for normal short-term fluctuations.
Why might one home reach 9 Bq/m³ while another reaches 30 Bq/m³?
Both can be excellent results. The final level depends on how radon enters the home and how completely the foundation can be depressurized and sealed.
Important factors include:
- Whether the basement is finished or unfinished
- How much of the slab edge, floor cracking, sump, and other entry points are accessible for sealing
- The material and airflow beneath the concrete slab
- The basement footprint and number of foundation levels
- The location and condition of an existing radon rough-in
- Weather, soil moisture, temperature, and barometric pressure
In an unfinished basement, ATMOS can usually access and seal more potential entry points. That often creates a more efficient system and may help the home reach especially low readings.
In a fully finished basement, much of the slab edge and floor may be concealed. The system can still reduce radon effectively, but readings in the 20 to 35 Bq/m³ range may be more typical than single digits. A result does not need to be zero to be successful—there is always some naturally occurring radon in outdoor air.
If a basement renovation is planned, it is an excellent time to test and, if necessary, mitigate. Completing the work before the floor and walls are covered gives the installer better access to seal entry points and route the system cleanly.
Will the radon reading stay exactly the same?
No. Daily and seasonal fluctuations are normal before and after mitigation.
Radon levels can change with:
- Outdoor temperature
- Barometric pressure
- Rainfall and soil moisture
- Heating and ventilation patterns
- Seasonal changes in the pressure difference between the home and the soil
A brief spike does not necessarily mean the system has failed. Look at the trend and the longer-term average rather than reacting to a single hourly or daily reading.
If the average remains above 75 Bq/m³ for several weeks, or the system monitor indicates that the fan is not creating suction, contact ATMOS so we can assess it. Do not switch off or adjust the system yourself.
How does the ATMOS results guarantee work?
ATMOS guarantees that a system we install will reduce the home’s long-term average radon level below 75 Bq/m³.
If appropriate follow-up testing shows that the long-term average remains above 75 Bq/m³, ATMOS will return, diagnose the system and foundation conditions, and make the modifications required to bring the installation into compliance with the guarantee.
The guarantee applies to the long-term average because that is the reliable way to evaluate ongoing exposure. A short-term reading can show that the system has begun working, but it cannot represent every season or condition in the home.
How does ATMOS verify the system after installation?
Before leaving the home, we verify that:
- The fan is operating
- The visible system components and connections are sealed
- The system is producing suction
- Air is discharging from the exterior exhaust
- The system monitor indicates normal operation
Within approximately 24 hours, we follow up with the homeowner to review the initial response. Many ATMOS customers own an electronic monitor and can watch the level fall. If they do not, we may leave a sensitive C-NRPP-approved measurement device in the home for several days to check the initial performance.
The first follow-up confirms that the system is responding as expected. Long-term testing confirms the result across normal changes in the home and weather.
What maintenance does a radon system require?
An active radon mitigation system is designed to operate continuously and requires very little routine attention.
Homeowners should occasionally check that the fan is running and that the system monitor remains in its normal position. Health Canada also recommends retesting a mitigated home at least every five years and after major renovations, changes to heating or ventilation, or alterations to the system.
ATMOS installations include a five-year fan warranty and a 10-year workmanship warranty. If a covered fan issue occurs during the first five years, or a covered workmanship problem affects the piping or installation during the first ten years, contact us and we will address it.
High radon is a problem with a proven solution
Discovering a high reading can be unsettling, but even very high radon can be reduced dramatically. A properly diagnosed and installed system works continuously in the background, uses little space, and requires minimal maintenance.
The goal is not to promise one exact number for every home. It is to create a reliable system, verify that it is working, and keep the home’s long-term average safely below the ATMOS guarantee of 75 Bq/m³.